These are cheap 4+1 VRMs, not even close to being built for pushing an x6 at 125W+. The heatsinks would probably help in keeping temps in check though at the very least. The likelihood is either that you are seeing OCP (Over Current Protection, present on some ASRock boards) kick in and downclocking your processor to save the VRMs, without you noticing; or you haven't had the combo long enough for it to fail yet (it can take time). IMO x6 shouldn't ever be overclocked on a 4+1 unless the quality has been proven, it is nicely heatsinked, AND it features OCP. The x6 is very heavy on the VRMs.